In recent years, advances in technology for developing a thin and light-weight display have generated a great deal of interest in materials for transparent electrodes.
Transparent conductive films have been generally used in advanced displays such as flat panel displays, touch screen panels, and the like.
For the flat panel displays, a transparent electrode can be formed by coating a metal oxide such as indium tin oxide (ITO) and indium zinc oxide (IZO) on a glass or plastic substrate via a coating process such as sputtering and the like.
The transparent electrode film formed using such a metal oxide has high conductivity and transparency, but also suffers low friction resistance and is vulnerable to bending.
Furthermore, indium adopted as one main material for the transparent film does not allow easy treatment and is very expensive due to limited natural reserves thereof.
Hence, the use of electrically conductive polymers, such as polyaniline, polythiophene, and the like, has been investigated to develop a transparent electrode that exhibits the beneficial properties of the polymers such as easy processibility and bending properties.
A transparent electrode film formed of a conductive polymer can have high electrical conductivity due to doping, good adhesion of a coating layer, and good bending properties.
However, the conductivity of the conductive polymer-based transparent film may not be sufficient for use as a transparent electrode, and the conductive polymer-based transparent film can have low transparency.
Carbon nanotubes have been developed as a material which can be used as a substitute for ITO. Carbon nanotubes are used in many fields. In particular, the use of carbon nanotubes as an electrode material exhibiting excellent electrical conductivity has been actively studied.
Carbon nanotubes are based on carbon and have a tube shape formed by rolling a graphite sheet in a spiral shape. As currently known in the related art, carbon-based materials include diamond, graphite, and fullerene. Compared with these carbon-based materials, carbon nanotubes have a lower density and exhibit higher strength, stability and electrical properties, thereby attracting considerable attention for use in many fields. In particular, the use of carbon nanotubes has been investigated for materials for field emission devices, light emitting devices, displays, and the like using the electrical properties of carbon nanotubes, and also composite materials for use as general materials.
For these applications, attempts have been made to enhance dispersibility and adhesive properties of carbon nanotubes to improve the electrical conductivity of the carbon nanotubes.
However, carbon nanotubes still do not have the conductivity of ITO (several tens of Ω/cm2).